Observations

Description

Valves are linear to linear-elliptical with rounded ends, which are slightly drawn-out. Raphe valve has narrow axial area, which widens into a small central area. Distal raphe ends are externally curved towards the same side of the valve and slightly expanded at their ends. Central raphe ends are slightly expanded externally, curved to opposite sides internally. Rapheless valve has narrowly linear axial area, which sometimes widens unilaterally into a small central area. Striae on both valves are biseriate. Areolae are elliptical or angular, transapically elongated. Internally areoale are covered by hymens. Striae are slightly radiate throughout both valves. Striae number 16-20 in 10 µm. Valve mantle bears one row of elongated areolae: there is one areola opposite to a stria, and one between striae.

Valves are linear-elliptical or elliptical with slightly drawn-out ends. The striae are slightly radiate throughout both valves and biseriate. The axial area is narrow. The central area is small, or absent. If present, it may be asymmetrical on the rapheless valve.

Compare

Rossithidium nodosum can be distinguished from A. minutissimum by its wider valves and broader striae. Achananthidium kriegeri possesses more narrow valves and an asymmetrical central area. Rossithidium pusillum is more broad, and is generally greater in length. The striae density is also greater (24 in 10 µm) and the striae are uniseriate.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

North American Diatom Ecological Database (NADED)

Autecology Discussion

reported from oligotrophic cold waters

Habits

Size Range

11-100 µm3 (ie Achnanthidium)

Motility

slightly motile (e.g. Cocconeis)

Attachment

prostrate (e.g. mucilage pad)

Habitat

benthic

Colony

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Rossithidium nodosum

Distribution

The distribution map represents the relative abundance of this Rossithidium nodosum in the western EMAP study. Relative abundance is a measure of the proportion of cells of this species based on a "fixed count" of 300 total diatom cells counted and identified. Each of the western EMAP sample sites is shown, either with a black dot for sites where Rossithidium nodosum was not recorded, or with a red circle indicating the relative abundance of Rossithidium nodosum.

Note that the size of the proportional symbols varies between species to help show both abundant and rare species.

Scale for the map to the left

EMAP Response Plots

Rossithidium nodosum

Responses

The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Rossithidium nodosum from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)STRAHLER = distribution plot of the Strahler Stream Order SLOPE = stream reach gradient (degrees)W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.PHSTVL = pH measured in a sealed syringe sample (pH units)log_COND = log concentration of specific conductivity (µS/cm)log_PTL = log concentration of total phosphorus (µg/L)log_NO3 = log concentration of nitrate (µeq/L)log_DOC = log concentration of dissolved organic carbon (mg/L)log_SIO2 = log concentration of silicon (mg/L)log_NA = log concentration of sodium (µeq/L)log_HCO3 = log concentration of the bicarbonate ion (µeq/L)EMBED = percent of the stream substrate that is embedded by sand and fine sedimentlog_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.